1. Technical Field of the Invention
The present invention relates to a coal ash treatment method and apparatus, and more particularly to the apparatus and the method for effectively utilizing fly ash and the like generated in coal firing power plants, etc. as a cement raw material while reducing mercury concentration in cement kiln exhaust gas.
2. Description of the Related Art
Fly ash generated in coal firing power plants or the like has been used for cement admixture, concrete admixture, raw materials for artificial lightweight aggregates, etc. In these cases, since fly ash containing much unburned carbon causes various problems it is necessary to remove the unburned carbon, so that many techniques have been proposed. Particularly, when fly ash is utilized for cement admixture, it is thought that adding wet ash that is obtained after decarbonization by wet flotation to a cement mill is the best method to reduce costs of equipment and operation.
Therefore, when utilizing fly ash as a cement admixture, the following method was adopted. The method comprises the steps of: generating slurry by adding water to fly ash; adding frothing agent to the slurry; generating air bubbles while agitating the slurry; causing unburned carbon contained in the fly ash to adhere to these air bubbles; removing the unburned carbon from the fly ash by removing the air bubbles; and grinding the fly ash together with clinker by a cement mill (exemplarily described in patent document 1).
Meanwhile, gas exhausted from a cement kiln contains an extremely small amount of metal mercury. Its origin is mercury contained in natural raw material such as limestone as a main raw material for cement as well as mercury contained in various kinds of recycle resources such as fly ash.
In recent years, recycle of wastes by converting to cement raw material and fuel has been promoted, and as the quantity of treated waste increases, mercury concentration in cement kiln exhaust gas has been increasing.    Patent document 1: Japanese Patent No. 3613347 gazette